Steemit itself is very different from Facebook and I can't see these two sites competing with each other. Just like Twitter is not fighting with YouTube, they serve different purposes.
However I see Steemit as a huge leap in social media site evolution, which might be the start which will grow something different to bring Facebook down from the position where it is now.
In my own words, facebook is more like a dictatorship while steemit is democracy... They might not compete but one is just way better than the other.
... wait, so which one is the better one? ;)
Some say that a great dictator is better than a mediocre democracy.
Haha, I believe everyone prefers to have a say in a matter than just being pushed around. And steemit is the democrat.